(1) Field of the Invention
The present invention relates to a moving sound source identifying system wherein an incoming direction of sounds emitted from a sound source, particularly a noise source, which is moving in a vertical plane or in a horizontal plane can be discriminated, and whether the sound source is moving or stationary can be identified.
(2) Description of the Prior Art
For the purpose of the identification of a moving sound source and the discrimination of the incoming direction of sounds emitted from the moving sound source in a conventional manner as shown in FIG. 1, a mountain-shaped variation of sound pressure levels of sounds, generally noises, emitted from the moving sound source, is simply measured. The sound pressure level variation is caused with the lapse of time in accordance with primary approach and secondary departure of the moving sound source relative to the measuring position. The time length .DELTA.T.sub.1 between the points whereon the sound pressure levels are reduced by a predetermined amount .alpha.dB from the peak of the aforesaid mountain-shaped variation, or the time duration .DELTA.T.sub.2 wherein the sound pressure levels exceeding a predetermined level can be obtained for identification.
However, the conventional manner as mentioned above has the serious defect that all of sounds emitted from various sound sources, which satisfy the above-mentioned conditions, are regarded as those emitted only from the same sound source, regardless of the types of the various sound sources, for instance, either a moving source or a stationary source, or, either a source flying in the sky or a source moving on the ground. Accordingly, even if it is desired to conduct the measurement only with respect to the noise emitted from an aircraft flying in the sky, similar results of the measurement can be obtained also with respect to the noise emitted from a vehicle, for instance, a motorcar, which is running on the ground close to the measuring position, so that it is impossible to identify the moving sound source, that is, the flying aircraft.
In order to more accurately identify a moving sound source a great many persons and hours must be used for the measurement, and, in addition various sound sources remain identified by means of an artificial measure, that is, the auditory sense.